sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling buggrafted

alb_break_llc() decides whether to break LLC preference during active
load balance. It does so by testing that every runnable fair task on the
source rq prefers its LLC:

	env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable

But the two counters cover different sets. nr_pref_llc_running is updated
in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued,
so it follows queued tasks. h_nr_runnable is updated in set_delayed()/
clear_delayed() and drops delay-dequeued tasks.

So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted
in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks,
alb_break_llc() returns false, and active balance is free to pull a task
off its preferred LLC. Active balance only moves runnable tasks, and this
is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB
skips the per-task test in can_migrate_task(). The runnable set is the one
we want.

Fix it on the counter side. A task should be counted in
nr_pref_llc_running exactly while it is both queued on its preferred LLC
(pref_llc_queued) and runnable (!sched_delayed). Define that membership
once in task_pref_llc_runnable(), and adjust the counter only through
pref_llc_running_inc()/pref_llc_running_dec() from the four sites that
change either input: account_llc_enqueue(), account_llc_dequeue(),
set_delayed() and clear_delayed(). Gating every update on the same
predicate keeps the delay, wake and dequeue paths from double-counting
or underflowing; see the comments at those sites for the ordering.

nr_llc_running and sd->llc_counts are not touched and stay on queued
semantics.

Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC")
Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/
Reported-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Suggested-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Kayra Cizmeci <kayracizmeci@gmail.com>
Cc: <stable@kernel.org> # v7.2.x
Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com

1 files changed, 198 insertions, 0 deletions

diff --git a/drivers/bluetooth/btrtl.h b/drivers/bluetooth/btrtl.h
new file mode 100644
index 000000000..a2d9d34f9
--- /dev/null
+++ b/drivers/bluetooth/btrtl.h
@@ -0,0 +1,198 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ *  Bluetooth support for Realtek devices
+ *
+ *  Copyright (C) 2015 Endless Mobile, Inc.
+ */
+
+#define RTL_FRAG_LEN 252
+
+#define rtl_dev_err(dev, fmt, ...) bt_dev_err(dev, "RTL: " fmt, ##__VA_ARGS__)
+#define rtl_dev_warn(dev, fmt, ...) bt_dev_warn(dev, "RTL: " fmt, ##__VA_ARGS__)
+#define rtl_dev_info(dev, fmt, ...) bt_dev_info(dev, "RTL: " fmt, ##__VA_ARGS__)
+#define rtl_dev_dbg(dev, fmt, ...) bt_dev_dbg(dev, "RTL: " fmt, ##__VA_ARGS__)
+
+struct btrtl_device_info;
+
+struct rtl_chip_type_evt {
+	__u8 status;
+	__u8 type;
+} __packed;
+
+struct rtl_download_cmd {
+	__u8 index;
+	__u8 data[RTL_FRAG_LEN];
+} __packed;
+
+struct rtl_download_response {
+	__u8 status;
+	__u8 index;
+} __packed;
+
+struct rtl_rom_version_evt {
+	__u8 status;
+	__u8 version;
+} __packed;
+
+struct rtl_epatch_header {
+	__u8 signature[8];
+	__le32 fw_version;
+	__le16 num_patches;
+} __packed;
+
+struct rtl_vendor_config_entry {
+	__le16 offset;
+	__u8 len;
+	__u8 data[];
+} __packed;
+
+struct rtl_vendor_config {
+	__le32 signature;
+	__le16 total_len;
+	__u8 entry[];
+} __packed;
+
+struct rtl_epatch_header_v2 {
+	__u8   signature[8];
+	__u8   fw_version[8];
+	__le32 num_sections;
+} __packed;
+
+struct rtl_section {
+	__le32 opcode;
+	__le32 len;
+	u8     data[];
+} __packed;
+
+struct rtl_section_hdr {
+	__le16 num;
+	__le16 reserved;
+} __packed;
+
+struct rtl_common_subsec {
+	__u8   eco;
+	__u8   prio;
+	__u8   cb[2];
+	__le32 len;
+	__u8   data[];
+};
+
+struct rtl_sec_hdr {
+	__u8   eco;
+	__u8   prio;
+	__u8   key_id;
+	__u8   reserved;
+	__le32 len;
+	__u8   data[];
+} __packed;
+
+struct rtl_subsection {
+	struct list_head list;
+	u32 opcode;
+	u32 len;
+	u8 prio;
+	u8 *data;
+};
+
+struct rtl_iovec {
+	u8  *data;
+	u32 len;
+};
+
+struct rtl_vendor_cmd {
+	__u8 param[5];
+} __packed;
+
+enum {
+	REALTEK_ALT6_CONTINUOUS_TX_CHIP,
+
+	__REALTEK_NUM_FLAGS,
+};
+
+struct rtl_dump_info {
+	const char *driver_name;
+	char *controller;
+	u32  fw_version;
+};
+
+struct btrealtek_data {
+	DECLARE_BITMAP(flags, __REALTEK_NUM_FLAGS);
+
+	struct rtl_dump_info rtl_dump;
+};
+
+#define btrealtek_set_flag(hdev, nr)					\
+	do {								\
+		struct btrealtek_data *realtek = hci_get_priv((hdev));	\
+		set_bit((nr), realtek->flags);				\
+	} while (0)
+
+#define btrealtek_get_flag(hdev)					\
+	(((struct btrealtek_data *)hci_get_priv(hdev))->flags)
+
+#define btrealtek_test_flag(hdev, nr)	test_bit((nr), btrealtek_get_flag(hdev))
+
+#if IS_ENABLED(CONFIG_BT_RTL)
+
+struct btrtl_device_info *btrtl_initialize(struct hci_dev *hdev,
+					   const char *postfix);
+void btrtl_free(struct btrtl_device_info *btrtl_dev);
+int btrtl_download_firmware(struct hci_dev *hdev,
+			    struct btrtl_device_info *btrtl_dev);
+void btrtl_set_quirks(struct hci_dev *hdev,
+		      struct btrtl_device_info *btrtl_dev);
+int btrtl_setup_realtek(struct hci_dev *hdev);
+int btrtl_shutdown_realtek(struct hci_dev *hdev);
+int btrtl_get_uart_settings(struct hci_dev *hdev,
+			    struct btrtl_device_info *btrtl_dev,
+			    unsigned int *controller_baudrate,
+			    u32 *device_baudrate, bool *flow_control);
+void btrtl_set_driver_name(struct hci_dev *hdev, const char *driver_name);
+
+#else
+
+static inline struct btrtl_device_info *btrtl_initialize(struct hci_dev *hdev,
+							 const char *postfix)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+
+static inline void btrtl_free(struct btrtl_device_info *btrtl_dev)
+{
+}
+
+static inline int btrtl_download_firmware(struct hci_dev *hdev,
+					  struct btrtl_device_info *btrtl_dev)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline void btrtl_set_quirks(struct hci_dev *hdev,
+				    struct btrtl_device_info *btrtl_dev)
+{
+}
+
+static inline int btrtl_setup_realtek(struct hci_dev *hdev)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int btrtl_shutdown_realtek(struct hci_dev *hdev)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int btrtl_get_uart_settings(struct hci_dev *hdev,
+					  struct btrtl_device_info *btrtl_dev,
+					  unsigned int *controller_baudrate,
+					  u32 *device_baudrate,
+					  bool *flow_control)
+{
+	return -ENOENT;
+}
+
+static inline void btrtl_set_driver_name(struct hci_dev *hdev, const char *driver_name)
+{
+}
+
+#endif